The present invention relates to Hall sensors for detecting spatial components of a magnetic field at a reference point, as well as to calibration and measurement methods used therein.
Apart from measuring magnetic fields with regard to amount and direction, Hall sensor elements based on the Hall-Effect are frequently used in the art, for contactless touchless signal generators for wearless detection of the position of switches or actuators. A further possible field of application is current measurement, wherein a Hall sensor element is positioned close to a conductive trace and measures the current in the conductive trace in a contactless manner by detecting the magnetic field generated by the current in the conductive trace. In practical application, Hall sensor elements have particularly shown to be useful due to their relatively strong insensitivity against outside influences, such as contamination, etc.
In the art, both the so-called horizontal or lateral Hall sensor elements and vertical sensor elements are known, wherein FIG. 9a exemplarily shows a horizontal Hall sensor element and FIG. 9b a conventional vertical Hall sensor element.
Generally, a Hall sensor element consists of a semiconductor die having four contact terminals provided for electrical connection to an external control circuit. Of the four contact terminals of a Hall sensor element, two contact terminals are provided for operating current impression by an active semiconductor region, while the other two contact terminals are provided for detecting the Hall voltage. If the operating current-carrying semiconductor die is exposed to a magnetic field having the induction {right arrow over (B)}, a deviation of the current paths results, which is caused by the “Lorentz force” acting on the moving charge carriers in the magnetic field. The Hall voltage results perpendicular to the direction of the current flow and perpendicular to the applied magnetic field in the active semiconductor region.
As basically shown in FIG. 9a, a conventional horizontal Hall sensor element 900 generally consists of an n-doped semiconductor region 902 on a p-doped semiconductor substrate 904. A Hall sensor element arranged in parallel to a chip surface (x-y-Level) is referred to as horizontal.
The n-doped active region 902 is normally connected to an external control or evaluation logic, respectively, via four contact electrodes 906a-d arranged in the active region 902 in opposing pairs. For reasons of clarity, the control or evaluation logic, respectively, is not illustrated in FIG. 9. The four contact electrodes 906a-d are subdivided into two opposing control current contact electrodes 906a and 906c, which are provided for generating a current flow IH through the active region 902, and further into two opposing voltage tapping contact electrodes 906b and 906d, which are provided for tapping a Hall voltage UH, which occurs with an applied magnetic field {right arrow over (B)} perpendicular to the current flow in the active region 910 and the applied magnetic field, as a sensor signal. By impressing the current flow IH between different contact electrodes and correspondingly tapping the Hall voltage UH at the other contact electrodes perpendicular to the current flow, compensation methods can be implemented, which allow the compensation of tolerances occurring in the Hall sensors, for example, due to production tolerances, etc, across several measurement cycles.
As can be seen from the horizontal Hall sensor element 900 illustrated in FIG. 9a, the active region is defined between the contact terminals 906a-d, such that the active region has an effective length L and an effective width W. The horizontal Hall sensor 900 illustrated in FIG. 9a can be produced relatively easily with conventional CMOS-processes (CMOS=Complementary Metal Oxide Semiconductor) for producing semiconductor structures.
Further, apart from the horizontal Hall sensor elements, implementations of the so-called vertical Hall sensor arrangements are known, which also allow the usage of the standard semiconductor production technologies, for example, CMOS-processes. One example of a vertical Hall sensor element 920 is basically illustrated in FIG. 9b, wherein vertical means a level perpendicular to the level of the chip surface (X-Y-level). In the vertical Hall sensor element 920 illustrated in FIG. 9b, the n-doped active semiconductor region 922 extends in the form of a well in a p-doped semiconductor substrate 924, wherein the active semiconductor region 922 has a depth T. As illustrated in FIG. 9b, the vertical Hall sensor element has three contact regions 926a-c, which are bordering on the main surface of the semiconductor substrate 924, wherein the contact terminals 926a-c are all within the active semiconductor region 922. Due to the three contact regions, this variation of vertical Hall sensor elements is also called 3-pin sensor.
Thus, the vertical Hall sensor element 920 illustrated in FIG. 9b has three contact regions 926a-c along the main surface of the active semiconductor region 922, wherein the contact region 926a is connected to contact terminal A, the contact region 926b is connected to contact terminal B, and wherein the contact region 926c is connected to a contact terminal C. If a voltage is applied between the two contact terminals. A and C, a current flow IH through the active semiconductor region 922 results, and a Hall voltage UH, which is perpendicular to the current flow IH and the magnetic field {right arrow over (B)}, can be measured at the contact terminal B. The effective regions of the active semiconductor regions 922 are predetermined by the depth T of the active semiconductor region 922 and the length L according to the distance between the current feeding contact electrodes 926a and 926c. 
Horizontal and vertical Hall sensors, as well as the methods for reducing offsets resulting from device tolerances, such as contaminations, asymmetries, piezoelectric effects, aging effects, etc, for example the spinning current method, are already known in literature, e.g. R. S. Popovic, “Hall Effect Devices, Magnetic Sensors and Characterization of Semiconductors”, Adam Hilger, 1991, ISBN 0-7503-0096-5. Vertical sensors operated by spinning-current frequently consist of two or four individual sensors, as it is for example described in DE 101 50 955 and DE 101 50 950.
Further, apart from the variation of the 3-pin vertical Hall sensor elements, there are so-called 5-pin vertical Hall sensor elements, which are also described in DE 101 50 955 and De 101 50 950. In the 5-pin Hall sensor elements there is also the possibility of performing a measurement compensated by tolerances of the individual devices with a compensation method extending across several measurement phases, for example, a spinning current method could be used here as well.
The spinning current technique consists of continuously cyclically rotating the measurement direction for detecting the Hall voltage at the Hall sensor element with a certain clock frequency, for example by 90°, and to sum it across all measurement signals of a full rotation by 360°. Thus, in a Hall sensor element having four contact regions, two of which are arranged in pairs, each of the contact pairs is used both as control current contact regions for current feeding and as measurement contact regions for tapping the Hall signal depending on the spinning current phase. Thus, in a spinning current phase or in a spinning current cycle, respectively, the operating current (control current IH) flows between two associated contact regions, wherein the Hall voltage is tapped at the two other contact regions associated to each other.
In the next cycle, the measurement direction is rotated further by 90°, so that the contact regions used for tapping the Hall voltage in the previous cycle are now used for feeding the control current. By summation across all four cycles or phases, respectively, offset voltages caused by production or material approximately cancel each other out, such that only the actually magnetic field dependent portions of the signals remain. This process can also be applied to a larger number of contact pairs, wherein, for example, with four contact pairs (having eight contact regions) the spinning current phases are cyclically rotated by 45°, in order to sum up all measurement signals across a full rotation by 360°.
In horizontal Hall sensors, four sensors are also frequently used, wherein, with an appropriate arrangement, the offset can additionally be heavily reduced by spatial spinning current operation, see e.g. DE 199 43 128.
If a magnetic field is to be measured for several spatial directions, mostly separate Hall sensor elements are used. The usage of separate sensors, for example for detecting the three spatial directions of a magnetic field, generally causes the problem that the magnetic field to be measured is not measured at one point, but at three different points. FIG. 10 illustrates this aspect, wherein FIG. 10 shows three Hall sensors 1002, 1004, and 1006. The first Hall sensor 1002 is provided for detecting a y-spatial component, the second Hall sensor 1004 for detecting a z-spatial component, and the third Hall sensor 1006 for detecting an x-spatial component. The individual sensors 1002, 1004, and 1006 measure the corresponding spatial components of a magnetic field approximately at the respective centers of the individual sensors.
An individual sensor can again consist of several Hall sensor elements. FIG. 10 shows exemplarily three individual sensors having four Hall sensor elements each, wherein in FIG. 10 exemplarily a horizontal Hall sensor 1004 is assumed, which detects a z-component of the magnetic field to be measured, and a vertical Hall sensor 1002 and 1006 each for the y- or x-component of the magnetic field to be measured. The arrangement for detecting the spatial magnetic field components, exemplarily illustrated in FIG. 10, has the problem that the magnetic field cannot be measured at one point, but at the respective centers of the individual sensors. This inevitably causes a corruption, since no exact evaluation of the magnetic field is possible based on the magnetic field components of the magnetic field sensors detected at different positions.
A further aspect of the detection and evaluation of the magnetic fields by Hall sensor elements is the calibration of the individual elements. Conventionally, Hall sensor elements are mostly provided with so-called excitation lines, which allow the generation of a defined magnetic field at the measurement point of an individual sensor, for subsequently obtaining calibration of the sensor by comparing or associating the measured Hall voltage to the defined magnetic field.
Excitation conductors allow the generation of an artificial magnetic field at a Hall sensor, which allows a simple wafer test, i.e. a test directly on the substrate as well as a self-test and a sensitivity calibration during operation, see Janez Trontelj, Optimization of Integrated Magnetic Sensor by Mixed Signal Processing, Proceedings of the 16th IEEE Vol. 1. This is particularly interesting in security critical areas, e.g. in the automobile industry or also in medical technology, since self-monitoring of the sensors is possible during operation.
If, for example, several individual sensors are used for detecting the spatial components of a magnetic field, as exemplarily shown in FIG. 10, every individual sensor necessitates a respective excitation line for calibration, and the individual sensors are further calibrated individually. It follows that the calibration effort scales with the number of individual sensor elements, and, in the case of spatially detecting three magnetic field components, the same is increased three times compared to the calibration effort of an individual sensor.
One approach for allowing an evaluation of a magnetic field, i.e. a measurement at one point, is a 3D sensor of the Ecole Polytechnique Federal Lausanne EPFL, cf. C. Schott, R. S. Popovic, “Integrated 3D Hall Magnetic Field Sensor”, Transducers '99, June 7-10, Sensai, Japan, VOL. 1, PP. 168-171, 1999. FIG. 11 schematically shows such a Hall sensor 1100, which is implemented on a semiconductor substrate 1102. First, the 3D sensor has four contact areas 1104a-d, across which currents can be impressed in the semiconductor substrate 1102. Further, the 3D sensor has four measurement contact areas 106a-d, via which the different magnetic components can be detected. A wiring 1110 is illustrated on the right-hand side of FIG. 11. The shown wiring composed of four operational amplifiers 1112a-d evaluates the Hall voltages proportional to the individual magnetic field components and outputs the respective components at the terminals 1114a-c in the form of signals Vx, Vy, and Vz.
The illustrated sensor has the problem that the same can only be calibrated by a defined externally generated magnetic field and has no individual excitation line. Further, due to its structure and its mode of operation, this sensor cannot be operated with the compensation method, e.g. spinning current method. Further, another problem of the structure shown in FIG. 11 is that such a semiconductor device has offset voltages due to contamination of the semiconductor material, asymmetries in contacting, variances in the crystal structure, etc., which cannot be suppressed by a respective spinning-current suitable compensation wiring. Thus, the sensor does measure magnetic field components at the focused point, but has a high offset and is thus only suitable for precise measurements in a limited manner. FIG. 12 shows a 3D sensor suitable for compensation (spinning-current), which detects spatial magnetic field components at a measurement point, and which is discussed by Enrico Schurig in “Highly Sensitive Vertical Hall Sensors in CMOS Technology”, Hartung-Gorre Verlag Konstanz, 2005, Reprinted from EPFL Thesis N° 3134 (2004), ISSN 1438-0609, ISBN 3-86628-023-8 WW 185 ff. The top part of FIG. 12 shows the 3D sensor of FIG. 10 consisting of three individual sensors. The upper part of FIG. 12 shows the three separate individual sensors 1002, 1004, and 1006 for detecting the spatial magnetic field components. The bottom part of FIG. 12 shows an alternative arrangement of the individual sensors. In this arrangement, the sensor 1004 remains unaltered, since the measurement point of the sensor 1004 is in the center of the arrangement 1200 in FIG. 12, further, the two individual sensors 1002 and 1006 consist of individual elements that can be separated. The sensor 1002 is now subdivided into two sensor parts 1202a and 1202b and arranged symmetrically around the center of the sensor element 1004. An analog method is performed with the sensor 1006, such that the same is also divided into two sensor parts 1206a and 1206b that are arranged symmetrically around the center of the sensor elements 1004, along the respective spatial axis. Due to the symmetrical arrangement of the individual sensor elements, the magnetic field is detected at one point, which lies in the geometrical center of the arrangement. One disadvantage of this arrangement is that the sensor can only be calibrated across several excitation lines. In the following, the arrangement 1200 in the bottom part of FIG. 12 will be referred to as pixel cell without calibration.